I have been trying to fix my crashing issue.
Didn't mention that my winform has a WPF usercontrol on it. Looking around I reckon that my issue is probably to do with that as there many other documented cases out there.
As a test I added a regular winform button to my main form and made it run the same code as the WPF button.Click the ordinary button and works ok, click the WPF button and it causes random crashes so for me that sort of proves that the WPF
The issue is similar to this posting I found "this is an access violation on WPF's render thread. Looking at this, we've seen similar crashes that were mainly due to a problem with the video driver. If you are seeing this only on a few machines, this is likely the case here as well"
I found this here : https://social.msdn.microsoft.com/Forums/vstudio/en-US/684b550f-80b4-4fe4-8cd2-b04f58dc50a5/wpf-control-embedded-in-winform-causes-outlook-crash-in-vsto-outlook-addin?forum=wpf